Transcript Introduction - Towson University

Welcome to COSC650
Towson University
Yanggon Kim
Fall 2009
COSC 650
1
Introduction
Outline
Statistical Multiplexing
Inter-Process Communication
Network Architecture
Performance Metrics
Implementation Issues
Fall 2009
COSC 650
2
Building Blocks
• Nodes: PC, special-purpose hardware…
– hosts
– switches
• Links: coax cable, optical fiber…
– point-to-point
– multiple access
Fall 2009
…
COSC 650
3
Switched Networks
• A network can be defined recursively as...
– two or more nodes
connected by a link, or
Fall 2009
– two or more networks
connected by a node
COSC 650
4
Strategies
• Circuit switching: carry bit streams
– original telephone network
• Packet switching: store-and-forward messages
– Internet
Fall 2009
COSC 650
5
Addressing and Routing
• Address: byte-string that identifies a node
– usually unique
• Routing: process of forwarding messages to the
destination node based on its address
• Types of addresses
– unicast: node-specific
– broadcast: all nodes on the network
– multicast: some subset of nodes on the network
Fall 2009
COSC 650
6
Multiplexing
• Time-Division Multiplexing (TDM)
• Frequency-Division Multiplexing (FDM)
L1
R1
L2
R2
L3
Fall 2009
Switch 1
Switch 2
COSC 650
R3
7
Statistical Multiplexing
•
•
•
•
•
On-demand time-division
Schedule link on a per-packet basis
Packets from different sources interleaved on link
Buffer packets that are contending for the link
Buffer (queue) overflow is called congestion
…
Fall 2009
COSC 650
8
Inter-Process Communication
• Turn host-to-host connectivity into process-to-process
communication.
• Fill gap between what applications expect and what the
underlying technology provides.
Host
Host
Application
Host
Channel
Application
Host
Host
Fall 2009
COSC 650
9
IPC Abstractions
• Request/Reply
– distributed file systems
– digital libraries (web)
• Stream-Based
– video: sequence of frames
• 1/4 NTSC = 352x240 pixels
• (352 x 240 x 24)/8=247.5KB
• 30 fps = 7500KBps = 60Mbps
– video applications
• on-demand video
• video conferencing
Fall 2009
COSC 650
10
What Goes Wrong in the Network?
• Bit-level errors (electrical interference)
• Packet-level errors (congestion)
• Link and node failures
• Packets are delayed
• Packets are deliver out-of-order
• Third parties eavesdrop
Fall 2009
COSC 650
11
Layering
• Use abstractions to hide complexity
• Abstraction naturally lead to layering
• Alternative abstractions at each layer
Application programs
Request/reply Message stream
channel
channel
Host-to-host connectivity
Hardware
Fall 2009
COSC 650
12
Protocols
• Building blocks of a network architecture
• Each protocol object has two different interfaces
– service interface: operations on this protocol
– peer-to-peer interface: messages exchanged with peer
• Term “protocol” is overloaded
– specification of peer-to-peer interface
– module that implements this interface
Fall 2009
COSC 650
13
Interfaces
Host 1
High-level
object
Protocol
Fall 2009
Host 2
Service
interface
Peer-to-peer
interface
COSC 650
High-level
object
Protocol
14
Protocol Machinery
• Protocol Graph
– most peer-to-peer communication is indirect
– peer-to-peer is direct only at hardware level
Host 2
Host 1
Digital
Video
File
library
application application application
RRP
Digital
Video
File
library
application application application
MSP
RRP
HHP
Fall 2009
MSP
HHP
COSC 650
15
Machinery (cont)
• Multiplexing and Demultiplexing (demux key)
• Encapsulation (header/body)
Host 1
Host 2
Application
program
Application
program
Data
Data
RRP
RRP
RRP Data
RRP Data
HHP
HHP
HHP RRP Data
Fall 2009
COSC 650
16
Internet Architecture
• Defined by Internet Engineering Task Force (IETF)
• Hourglass Design
• Application vs Application Protocol (FTP, HTTP)
FTP
HTTP
NV
TFTP
UDP
TCP
IP
NET1
Fall 2009
NET2
COSC 650
…
NETn
17
ISO Architecture
End host
End host
Application
Application
Presentation
Presentation
Session
Session
Transport
Transport
Network
Network
Network
Network
Data link
Data link
Data link
Data link
Physical
Physical
Physical
Physical
One or more nodes
within the network
Fall 2009
COSC 650
18
Performance Metrics
• Bandwidth (throughput)
– data transmitted per time unit
– link versus end-to-end
– notation
• KB = 210 bytes
• Mbps = 106 bits per second
• Latency (delay)
– time to send message from point A to point B
– one-way versus round-trip time (RTT)
– components
Latency = Propagation + Transmit + Queue
Propagation = Distance / c
Transmit = Size / Bandwidth
Fall 2009
COSC 650
19
Bandwidth versus Latency
• Relative importance
– 1-byte: 1ms vs 100ms dominates 1Mbps vs 100Mbps
– 25MB: 1Mbps vs 100Mbps dominates 1ms vs 100ms
• Infinite bandwidth
– RTT dominates
• Throughput = TransferSize / TransferTime
• TransferTime = RTT + 1/Bandwidth x TransferSize
– 1-MB file to 1-Gbps link as 1-KB packet to 1-Mbps link
Fall 2009
COSC 650
20
Delay x Bandwidth Product
• Amount of data “in flight” or “in the pipe”
• Usually relative to RTT
• Example: 100ms x 45Mbps = 560KB
Delay
Bandw idth
Fall 2009
COSC 650
21
Socket API
• Creating a socket
int socket(int domain, int type, int protocol)
• domain = PF_INET, PF_UNIX
• type = SOCK_STREAM, SOCK_DGRAM,
SOCK_RAW
• Passive Open (on server)
int bind(int socket, struct sockaddr *addr, int addr_len)
int listen(int socket, int backlog)
int accept(int socket, struct sockaddr *addr, int addr_len)
Fall 2009
COSC 650
22
Sockets (cont)
• Active Open (on client)
int connect(int socket, struct sockaddr *addr,
int addr_len)
• Sending/Receiving Messages
int send(int socket, char *msg, int mlen, int flags)
int recv(int socket, char *buf, int blen, int flags)
Fall 2009
COSC 650
23